Telegraph exchange system



May 14, 1946. l G, U HT 2,400,124

I TELEGRAPH EXCHANGE SYSTEM Original Filed July 51 1941 5 Sheets-Sheet lF :uu: Hnnr! T v r a g *Hll l m l 1 E INVENTOR L l T :Q) 1' s. c. LIGHTi I o D N man aY w ATTORNEY -TO FIG. 4

3 1946- e. s. LIGHT 2,400,124

TELEGRAPH EXCHANGE SYSTEM Original Filed July 31 1941 5 Sheets-Sheet 2ATTORNEY May 14, 194-6. UGHT 2,400,124

' TELEGRAPH EXCHANGEVSYSTEM Original Filed July 51 1941 5 Sheets-Sheet 3FIG. 3

Eii

INVENTOR e. c. LIGHT {ll U l H: ATTQRNEY May 14, 1946. LIGHT TELEGRAPHEXCHANGE SYSTEM Original Filed July 51 1941 5 Sheets-Sheet 4 BY ATTORNEYm (PM i N vu.

TO FIG.5

Patented May 14, 1946 2,400,124 TELEGRAPH EXCHANGE SYSTEM George G.Light, Kew Gardens, N. Y., assignor to The Western Union TelegraphCompany, New York, N. Y., a corporation of New York Original applicationJuly 31, 1941, Serial No.

404,765. Divided and this application March 24, 1943, Serial No. 480,264

. 12 Claims. Cl. 178-2) This invention relates to telegraph systems andmore particularly to multi-station printing telegraph systems embodyinga plurality of stations or oifices and arrangements for selectivelyinterthe transmission of code signals to the line through theswitchboard.

Another object of the invention is to provide a system as outlined abovewhich is capable of connecting the transmitting and receiving ap- 5,operating in conjunction with a multistation or paratus or printers ofthe system. The present way-station circuit in such a manner that theinvention involves an improvement in or modifi central ofilce'may selectany one of the stations cation of the telegraph systems shown in the. onthe way-station and lock out the unselected patent to Wheeler, Hooverand Dirkes, No. stations.

2,193,810, granted March 19, 1940, and in the V In accordance with theabove, another object pending application of G. G. Light and W. B. ofthe invention is to provide means whereby the Blanton, Serial No.350,402, filed August 3, 1940, selection of a station on a way-stationcircuit is and is a division of the application of G. G. Lightautomatically effected from the central station by Serial No. 404,765,filed July 31, 1941, now Patent a plugging operation into one or-theother of a No. 2,351,621, granted June 20, 1944. plurality of jacks,each individual to one of the In general terms, the object of thisinvention stations on t e way-station circuit. is to simplify theselecting and control apparatus A still further object of the inventionis to proin systems of the above-mentioned character, and vide a systemof the above type embodying the guard against faulty operation, as forexample above enumerated features operating in consending to a stationwhere the receiving appara- 0 junction with a central ofiice wherein thereceivtus is not conditioned for operation or has been ing equipmentthereat is in a concentrator ardisconnected. Heretofore codetransmittersand rangement. code-responsive equipment have been commonlyQther objects and advantages of the invention employed for selectingstations, operating signals will appear from the followin description ofthe and motor controls, and eifecting other functions preferredembodiment thereof shown in the acin a multi-station system. The controlequipment companying drawings, wherein: in some instances is quitecomplex, and the sys Fi s. 1, 2 and 3 taken together constitute a ternistfutlgher ctomlplicateld ts it neccsigry to wiring diagram of asingle-station line circuit and sepala e e 0011 r0 Sigma 5 Tom 6 prm theterminal equipment at the main station or nals which are ordinarily sentover the same line switching t circuitsm Pystems, the character of theFigs. 4 and 5 form a wiring diagram of a multitelegraph 11116? llmltsthe character of the station or way-station circuit, also terminating intronmg code S1gna1s that P usedone the equipment at the main stationshown in Figs. ture of the present invention 18 anovel arrangeor 2 and3; ment fill effecting station selecttion, for selzting m) 6 is a timingchart illustrating the and re eaS1 ng prmtntg or tepea appam ferredtiming adjustments of the various timing and operating supervisorysignals or other funcunits. and tions over the line circuit withoutemploying V g. 7 illustrates the manne1 in which Figs. 1 ell/hi1 codetransmitters or code-responsive equlpto 5 are arranged to form thomplete circuit i other obect of the invention is to nterlocl: diagramthe sending and receiving apparatus in a tele- In t t l an eyf'changesystem. is Shown graph exchange system, wherein the transmitting m i gsmile q q Y m: statlqn apparatus at a main station or switching centerI, a fi t clrcu S a a 2 may be temporarily connected with an outgoing S3 Ion SW1 0 mg f er SW1 0 line, in order that line circuitinterruptionsmay mi for ntterconneitltlg P11311118 clrcults' the betransmitted for signaling and control purposes remote stations, a cal 1simtiated by actuating a calling key and terminated by restoring saidkey. from a remote station to the switching center and vice versa,irrespective of connections made to a r The opFratlPn of caumg W calls?a line at the switchboad in the Switching centen determined interruptionof the line circuit to the w this feature f the invention, t, becomesmain station which is effective to pick up an idle possible to transmitcontrol circuit-interruptions storage and trans i g l AS soon as an idleof predetermined length in both directions over mill; is eized, a 11118c1rc u1t interruptionof a D the'line circuit without the possibility ofthe dura- I determined length is produced at the main station tion ofthe signals being altered or distorted by which is efiective to operatea go-ahead signal at the remote station. If the line circuit becomesopened or the storage equipment accidentally disconnected, the go-aheadsignal at the remote station is extinguished or restored to indicate atsaid station that transmission should be stopped. At the end of themessage, the release and restoration of equipment are also accomplishedby the transmission of line circuit interruptions of 'predeterminedlength, and certain guard features are incorporated, as will be pointedout hereinafter.

In the case of a multi-station or way-station line circuit, theinitiation of a call from one of the remote stations to the main stationlocks out the other station and also initiates a call to the mainstation in substantially the same manher as in the case of the singlestation circuit. In making an outgoing connection to the waystationcircuit at the switchboard, the desired station is selected by thetransmission of a, line circuit interruption, of different length foreach station on said circuit. The selecting interruption signal isautomatically produced upon plugging into one or the other of aplurality of jacks, each individual to one of the stations in the Waystation circuit. At the end of the call, the circuit is released and thecontrol equipment automatically restored to normal, a "clear-out circuitinterruption signal being transmitted to the remote stations from themain office as in the case of a call to or from a station on thesingle-station line circuit.

Single-station Zine circuit Referring to Figs. 1, 2 and 3 of thedrawings, the printer PI at station A, Fig. 1, is connected through theline LI to the main olfice where messages received from station A may berecorded or stored and retransmitted over outgoing lines or channelsterminating at said office at the switchboard represented by the jacks JIJ 4, Fig. 3. Messages received from station A at the main office andfrom the other stations over lines terminating at said ofiice are storedin the form of perforated tape in the receiving reperforators such asthat shown at RR, Fig. 2, and repeated by the associated tapetransmitter TT after the tape transmitter has been plugged into the jackrepresenting the selected outgoing line circuit or channel substantiallyas described in the abovementioned copending application of Light andBlanton. The tape transmitter may be similar to that shown in the patentto Angel, No. 2,172,269, dated September 5, 1939. The reperforator maybe a printer perforator similar to that shown in the patent to Dirkesand Wentworth, No. 2,143,- 828, dated January 10, 1939. When one of theremote stations, such as the station A, initiates a call to the mainoffice, a finder switch SI or S2 is operated to connect an idlereceiving reperforator RR to the calling line in a manner to bedescribed below. This general arrangement including a series of finderswitches for connecting an idle receiving unit or a reperforator to acalling line is shown in a number of patents in the prior art includingthe above-mentioned patent to Wheeler et al. The arrangement shownherein is conventional except for certain features to be described, andtherefore certain details of construction are omitted for the sake ofsimplicity.

The line LI may be any suitable telegraph channel but for purposes ofillustration it is shown as terminating at the respective ofiices orstations in terminal duplex sets II and I2 of a conventional character.The keyboard of the printer PI is connected to the sending leg of theterminal duplex set I l and the printer magnet is connected to thereceiving leg thereof in series with a normally operated relay I3. Thesending leg of the terminal duplex set I2 at the main office isconnected through the back contacts of relay I4 to the switchboard,while the receiving leg is connected through the conductor I5 andcontacts of relay 26 to the winding of relay 25. The energization ofrelay 26 when the finder switch SI has connected to the calling linedisconnects relay 25 from the receiving leg which is then connectedthrough conductor I5 and the finder switch to the selector magnet of thereperforator RR.

When it is desired to initiate a call from station A to the main ofiiceor to one of the lines or channels terminating at the switchboard in themain office, the key I8 is actuated, thus closing a circuit frompositive battery through the outer left hand contacts of the key I8,condenser I9 and shunt resistor 20 to the right hand winding of relay2!. The charging current of the condenser I9 causes relay 2I to attractits armatures momentarily, thus opening the line circuit extending fromground through the inner armature and back contact of said relay, theleft hand armature and back contact of relay 49 in shunt relation to thekeyboard contacts of the printer PI, and the winding of the transmittingrelay 22. The operation of the transmitting relay 22 momentarily opensthe rest or marking contacts of the differential relay of the terminalduplex set I2 at the main oflice, thereby opening the circuit of thenormally operated relay 25, and said relay becomes deenergized. Upon thedeenergization of relay 25, a circuit is closed through the left handarmature and back contact of said relay and the left hand armature andback contact of relay 26 in shunt relation to the winding of relay 25,thereby short-circuiting relay 25 to prevent the attraction of thearmatures of said relay when the line circuit is reclosed. Thedeenergization of relay 25 closes a circuit through its right handarmature and back contact for initiating the operation of the first idlefinder switch SI, S2, and so forth, to connect the associated idlereperforator to the line extending to the calling station A. AS pointedout above, this general arrangement is well known in the art and variousarrangements for distributing successive calls to idle receiving unitsor reperforators may be employed. As shown, the grounding of theinitiate conductor 28 by relay 25 closes a circuit through the innerleft hand armature and back contact of relay 29 and the right handwinding of relay 32 to battery, assuming that the receiving reperforatorRR is idle. If the reperforator RR is in use, relay 29 will be operatedto transfer the initiate circuit to the next finder switch S2, as shown.

The energization of relay 32 closes a circuit to the stepping magnet 33of switch SI, which circuit may be traced through the right handarmature and front contact of relay 32, the left hand outer armature andback contact of relay 29 and the upper wiper of the switch SI to thegrounded bank contacts representing idle lines or lines which arealready connected to a receiving reperforator and are thus groundedthrough the wipers of other finder switches. When the stepping magnet 33of the switch SI, which is provided with self-interrupting contacts, asshown, has actuated the wipers of the switch into engagement with thebank contacts representingthe calling line, in this instance the firstbank contacts, the stepping of the switchstops, since the bank contactassociated with the upper wiper is no longer grounded through theconductor 34 and the front contact associated with the right handarmature of relay individual to calling station A. Thereupon the shortcircuit around relays 29 and 32 is opened, and relay 29 becomesenergized through a circuit from battery through the stepping magnet 33,the left hand armature and front contact and left hand winding of relay32, the left hand Winding of relay 2 9, and the armatures and backcontacts of relays 36and 31 to ground. Relay 32 is locked up in serieswith the left hand winding of relay 29. Since the stepping magnet 33 isof low resistance compared to the windings of relay 29 and 32, thecurrent through the stepping magnet is insufiicient to actuate theswitch wipers at this time.

The energization of relay 29 as described connects ground potentialthrough the outer left hand armature and front contact thereof to thebank contact associated with the upper switch wiper of the switch SI toprevent another of the finder switches from connecting to bank contactsmultipled to the first contacts of switch Si. The energization of relay29 transfers the initiate circuit through its left hand inner armatureand front contact to the control relays associated with the second witchS2 so that the next succeeding call will be picked up by the secondstorage unit until the first storage unit has been released. Theenergization of relay 29 also closes a circuit through its second righthand armature and front contact, the middle wiper of the switch SI,conductor 39, the winding of relay 26 and the right handarmature andfront contact of normally energized relay 21 for energizing relay 26.The energization of relay 2B closes the circuits of relays 25 and at,the right hand inner and middle contacts of said relay, and relays 25and 30 become energized. The energization of relay 26 also opens at itsouter right hand armature and back contact the circuit of slow releaserelay 21, and after a short interval the latter relay releases itsarmatures. The energization of relay 30, as described, removes groundpotential from the conductor extending to the jacks J l and J2 of theswitchboard individual to the line Ll As indicated, the conductor 40forms a part of the clutch magnet circuit of any distributor(corresponding to the circuit of the clutch magnet 63 of the distributorshown in Fig. 2) when the associated transmitter is plugged into thejack J I or J2. Thus, the energization of relay 30, indi-; vidual to theline Ll, stops transmission from the main office over said line topermit control signals or line interruptions, to be transmitted tostation A. Similar relays are associated with the switchboard circuitsof each full duplex line to stop transmission from the main officemomentarily while an incoming call is being set up or disconnected overthe same line. The slow-release relay 21 is adjusted so that it does notrelease its armatures until the lapse of sufficient time to insure thatthe cam shaft of the distributorcontrolled by relay 30 has come to rest.I In order to indicate to the operator or attendant at station A that acomiection to the receivingreperforator has been established andtransmission may be commenced, the rest or marking line condition isinterrupted for a predetermined period at the main oflica' ,This isaccomplished as follows: Upon the deenejrgization of relay 21 asdescribed, the short circuit around the right hand winding of relay 4|is opened, and said relay becomes energized in series with relay 26.Thereupon a circuitis closed from ground through the left hand outerarmature and back contact of relay 42, the left hand outer armature andfront contact of relay 4| and the winding of relay I4 to positivebattery, whereupon relay 14 becomes energized to open the sending leg ofthe terminal duplex set l2, which operates the receiving differentialrelay of the terminal duplex set II at station A, causing relay l3 tobecome deenergized. At the same instant the energization of relay 4|opens the connection from negative battery to the grid .of a Vacuum tube43 having the plate circuit thereof connected to the winding of relay42. The vacuum tube 43 constitutes a timing device for operating relay42 after a predetermined lapse of time, and for this purpose, the gridcircuit of the tube 43 is provided with a shunt condenser 44 and gridleak 45 so that the potential of the grid of said tube gradually driftstoward the ground or open-:circuit potential whenever the negativecut-off potential has been removed from the grid by the operation ofrelay 4 I. Thus,

after a predetermined time delay which may be only a fraction of asecond, relay 42 becomes energized and opens at its outer armature andback contact the above-described circuit of relay M. The deenergizationof relay l4 recloses the line circuit so that the line interruption isaccurately timed by the characteristics of the grid circuit of thevacuum tube 43. The operation of relay 42 also opens the circuit ofrelay 30, and said relay recloses the clutch magnet circuit 43, thuspermitting transmission over the line Ll through the switchboard to beresumed.

At station A, the deenergization of relay l3 as described removesnegative cut-off potential from the grid of the slow-to-operate ortiming vacuum tube 48 and, after a predetermined period of time slightlyless than the length of the line interruption caused by the timing tube43, current flows through the vacuum tube 48 to energize the associatedrelay 49 and light the supervisory lamp 50 to indicate to the attendantat station A that the connection to the idle reperforator has beencompleted and transmission may be commenced. The vacuum tubes 48, 5! and52 at station A and tube 53 at the main office are all arranged like thetube 43 to impart a delayedoperating characteristic to the relay in theplate circuit thereof by control of the grid potential as describedabove, but the timing of the vacuum tubes is fixed at different periodsfor the purposes to be pointed out below. By Way of exam-- ple, suitabletiming adjustments for the respective timing control units are shown inFig. 6.

Upon the energization of relay 49 as described, a locking circuit forsaid relay is closed through its right hand inner armature and frontcontact and the inner armature and back contact of relay 56. A circuitis also closed through the right hand middle armature and front contactof relay 49, the armature and back contact of relay 55, the left handwinding of relay 2i and the right hand inner contacts of the key l8whereupon relay 2| becomes energized and removes ground potential at theinner armature and back contact thereof from the keyboard of placed inoperating condition, the line circuit through the keyboard contactsbeing connected through the left hand armature and front contact ofrelay 49 to ground at the left hand inner contacts of the key H3. Theoperation of the keyboard of the printer Pl transmits alternate rest ormarking and spacing permutation code signals over the line Ll, thesignals being transmitted through the conductor l5 and the contacts ofthe receiving relay of the terminal duplex set I2 at the main oflice andthe contacts of the lower wiper of the switch S| to the magnet of thereceiving reperforator RR, which records the received message in theform of perforated tape adapted to operate an associated tapetransmitter TT to repeat the signals through the selected outgoing linecircuit of channel.

After transmission has been completed the operator or attendant atstation A releases the connected storage and transmitting equipment byrestoring the key I8. If the operator fails to restore the key |8 at theend of the message or if, for any reason, no message signals aretransmitted for, say thirty seconds, the timing vacuum tube 64 becomesconducting at the end of the selected period and relay 36 in the platecircuit of said tube is energized. The energization of relay 3B releasesrelays 29 and 32 to release the switch SI and transmit a disconnectsignal to station A in a manner described below in connection with thenormal disconnect operation. This feature of the invention prevents theoperator at a calling station from tying up a reperforator indefinitely,but it will be noted that release of the switch in this manner will notbe effected if the line circuit goes open, as in that case the seriesline relay 3| remains deenergized and maintains a negative cut-offpotential on the grid of vacuum tube 64. Upon the restoration of the keyl8 at the end of a message, the line circuit including the winding ofthe transmitting relay 22 and the left hand inner contacts of the key I8is opened and at the same moment, the negative cut-off bias potential isremoved from the grid of the vacuum tube 5|. After a predetermined timeinterval, current flows through vacuum tube 5| and the relay 55 in theplate circuit thereof becomes energized. The energization of relay 55opens the circuit of the left hand locking winding of relay 2| and saidrelay becomes deenergized, thereby reclosing the line circuit includingrelay 22.

The timing of the line interruption as described is adjusted byemploying suitable characteristics for the condenser and leak in thegrid circuit of the vacuum tube 5| so that its duration is equal inlength to transmission of one character from the keyboard of the printerPl. Therefore, the receiving reperforator RR at the main ofiice respondsas though a "blank or all-spacing code combination had been transmitted,and the blank-reading contacts 59 on the reperforator will momentarilyclose. The construction of a reperforator having contacts closed uponthe reception of a particular code combination, for example, a blank, isdisclosed in the above-mentioned Dirkes and Wentworth patent. Thecontacts could be applied to the stop member for the blank selection ifthe sixth pulse cutout was omitted. The closure of contacts 59 effectsrelease of the finder switch SI in a manner to be described. Upon theoperation of relay 55 as described above, the circuit of the left handor looking Winding of relay 2| is opened and the latter relay becomesdeenergized. Negative cutoff potential is connected through the outerarmature and back contact of relay 2| to the bridge circuit of thevacuum tube 5| whereupon relay 55 becomes deenergized. All relays exceptrelay 49 at station A are now restored to normal but the supervisorylamp 5%] remains lighted through a contact of relay 49 until finderswitch S| at the main oifice has been restored to normal. The purpose ofthis arrangement will be described hereinafter.

The closure of the blank-reading contacts 59 of the reperforator at themain oiiice closes the circuit of relay 30 and at the end of the blankthe line relay 3| which responds to line ignals is reenergized to closea circuit through its armature and front contact and the left handarmature and front contact of relay 60 for operating disconnect relay31. The energization of relay 3'! interrupts the circuit through theleft hand windings of relays 29 and 32 and said relays becomedeenergized, thus restoring the selector switch SI to normal inreadiness for the next call. Upon the deenergization of rela 29, thecircuit of rela 26 is opened at the second. right hand armature andfront contact of relay 29. The deenergization of relay 26 operates relay30 to stop transmission over the line Ll from the main office Whiletransmitting the break signal of such duration as to extinguish thesupervisory lamp 5|] at the remote station A. The circuit of relay 30may be traced through the middle right hand armature and back contact ofrelay 25 and the inner armature and front contact of relay 42. Theenergization of relay 30 opens the circuit of the clutch magnet of thetransmitting distributor of any transmitter which may be connectedthrough the switchboard to the line L! as described above, Thedeenergization of relay 26 further opens at its outer right handarmature and front contact the circuit of slow relay 2? and, after ashort interval sufficient to permit the cam shaft of the sendingdistributor to come to rest, relay 2'! releasesits armatures. Upon thedeenergization of relay 21, the circuit of relay 3-5 is interrupted atthe left hand armature and front contact of the firstmentioned relay,and relay 35 becomes deenergized. Upon the deenergization of relay 35, acircuit is closed through the inner armature and back contact of saidrelay, the outer armature and front contact of relay 42 and the outerleft hand armature and front contact of relay 4| for operating relay Mto interrupt the line circuit at station A at the same instant thatnegative cut-off potential is removed from the grid of vacuum tube 53 atthe outer armature and front contact of relay 35. After a predeterminedtime interval fixed by the characteristics of the grid circuit of thevacuum tube 53, current flows through the winding of relay 54 in theplate circuit thereof and said relay becomes energized. Upon theenergization of relay 54 the circuit of the left hand locking winding ofrelay 4| is interrupted, whereupon said relay becomes deenergized andopens the above-described circuit of relay |4. The deenergization ofrelay I4 recloses the line circuit. Upon the deenergization of relay 4|,negative cut-off potential is applied through the right hand armatureand back contact of said relay to the grid of the vacuum tube 43whereupon relay 42 becomes deenergized and opens the circuit of relay30. Upon the deenergization of relay 3!], the sending distributor of thetransmitter plugged into the line Ll is again rendered operative fortransmission. 1

At station A, the line relay I3 in the receiving leg of the terminalduplex set I I becomes deenergized in response tothe opening of the linecircuit by the operation of relay M, as described above, therebyremoving negative cut-ofi potential from the grids of vacuum tubes 48and 52. After a predetermined time interval long enough to permit bothtubes 48 and 52 to become conductive but slightly shorter than thetiming of vacuum tube 53 at the main ofiice, current flow is establishedthrough the tubes 58 and 52, and their associated relays 49 and 56respectively. Since relay 49 was previously locked up through its innerright hand armature and front contact, it remains energized until relay56 becomes energized. Upon the energization of relay 56 the circuit ofrelay 49 is interrupted and said relay becomes deenergized to therebyextinguish the lamp 50. At the end of the line circuit interruption,relay l3 again becomes energized and connects negative cut-off potentialthrough its armatures and front contacts to the grids of tubes 48 and52, thereby deenergizing relay 56 and maintaining relay 49 deenergized.

It will be noted that an important feature of the invention is theoperation of the supervisory lamp 5!) solely' under the control of thefinder switches at the main ofiice, the lamp being lighted as soon asone of the switches has seized an idle reperforator and beingextinguished, not by the disconnect key l8, but when the finder switchhas been released. Thus, if a false or accidental blank signal isreceived at the main office owing to line or apparatus trouble, whichwould cause the switch to release the connected reperforator, thesupervisory lamp 50 will become extinguished to indicate that thereceiving unit at the main office has been disconnected. Similarly, ifthe receiving reperforator is disconnected either by the operation ofthe relay 36 as described above or in any other manner by an attendantat the main oflice, for-example, the supervisorylamp 50 would serve as apositive indication to the operator or attendant at station A tostopsending until the line has been connected to another receiving unit.

As shown, the printer Pl at station A does not respond to its ownkeyboard to make a home copy of the messages transmitted from thestation but is always in readiness to respond to transmission from themain oifice. However, on lines which are not arranged for full duplex operation, the printer magnet may be connected in series with the keyboardas usual, Since the keyboard contacts are short-circuited by relay 49when the receiving reperforator at the main office becomes disconnected,the failure of the printer to function provides an immediate signal tothe operator that the circuit is not in readiness for-transmission;

Way station circuit The operation of a way station circuit where aplurality of stations are connected through a single series line circuitto the main station includes additional features not embodied in thesingle station circuit described above. Stations B and 0, Figs. 4 and 5,are shown connected to a line circuit L2, which terminates at the mainstation in the finder switches SI? and S2, as inthe case of the line Ll.For the purposes of illustration, the line L2 is arranged for halfduplex operation, providing for transmission from either of thestationsB and C to the main office or switching center or fortransmission from the switching center to either of said stations, butnot for transmission in both directions at the same time. Thisillustrates the flexibility of the control system provided by theinvention which will operate over either a half duplex, a full duplex(single-station operation), or any normally closed circuit adapted totransmit telegraph signaling impulses.

The operation of the Way station circuit is generally similar to that ofthe single station circuit described aboveexcept that provisions aremade for operating a busy signal and looking out one of the remotestations when a call is initiated to the main station from the otherremote station, and means is provided at the main office or switchingcenter for selectively calling either of the remote stationsand lockingout the other station. In the idle line condition, the printers P2 andP3 at stations B and C, respectively, are non-responsive to linesignals, since the printer magnet is connected to holding ground. Inview of the fore going detailed description of Figs. 1 to 3, thedescription of the operation of the way station circuit will be directedto these additional features. Assuming that the line circuit is idle andthat the operator or attendant at station B desires to initiate a callto the main office or transmit a message through the main officeswitchboard to an outgoing line or channel, upon the operation of thecalling key 10, relay H becomes energized to interrupt the line circuitat the left hand armature and back contact of said relay to initiate theoperation of one of the finder switches SI or S2, as described above inconnection with Figs. 1, 2 and3. In this instance, however, instead of aline interruption of indeterminate length, the duration of the lineinterruption is timed in order to lock out the printer-P3 and operate abusy signal at'station C.

The circuit of relay ll may be traced through the left hand armature andback contact of relay 12 the right hand inner armature and back contactoffrelay 13,the third left hand armature and back contact of relay 14,the right hand make contacts of the-key 10, the outer armature and backcontact of relay 15, the winding of relay H, and the middle left handarmature and back contact of relay 1E. Relay H locks up through itsright hand inner armature and front contacts to ground at'the right handarmature and back contact of relay 12. The opening of th line circuit byrelay H closes the back or spacing contacts oi the line relay 11, thusclosing a circuit through said contacts, the winding of relay 13 and theright hand winding of the normally operated relay 19 for operating relay18. The energization of relay .18 removes negative cut-off potentialfrom the grid of the timing tube to cause the operation of theassociated relay 16 after a predetermined time interval fixed by thecharacteristics of the grid circuit of said tube. Thetiming units ortubes 80, 8|, 82, 83, as well as the other vacuum tubes shown at themain office and station C, are similar in arrangement and operation tothose described above in connection with Figs. 1 and 2, and thetimingcharacteristics of the tubes are shown in Fig. 6. The grid circuitof the vacuum tube 80, however, further includes a tapped leak resistorwhich is operative to change the timing of the associated tube dependingupon whichtap on the resistor is connectedto ground, as obviously theless resistance that is connected in shunt to the grid condenser, themore rapidly the charge on the condenser will be equalized'to permit theassociated tube to become conducting. During the sending of the callingsignal, the taps on the resistor 85 are ungrounded; thus delaying theoperation of the tube 80 and relay IE to the maxi mum extent. When thetube 80 becomes conducting, relay I6 in the plate circuit thereofbecomes energized, locks up, and at its left hand middle armature opensthe circuit of relay II, whereupon the line circuit is reclosed. RelayI6 also opens the circuit of relay I9, thus removing holding ground fromprinter P2. The reenergization of the line relay 11 causes thedeenergization of relay I8 and the tubes 8|, 82 and 83 are renderedineffective.

The line interruption initiated as described above and transmittedthrough the duplex sets 81 and 88 operates the armature of thedifferential relay of the duplex set 88 to spacing, thus opening thecircuit of the line relay 90, and said relay becomes deenergized. Acircuit is closed from ground through the armature and back contact ofrelay 9!], the winding of relay 9|, and the inner left hand armature andback contact of relay 92 to battery, whereupon relay 9| becomesenergized and locks up through its right hand inner armature and frontcontact to a circuit that is independent of the contacts of relay 90.

The energization of relay 9| closes a circuit through its left handarmature and front contact for energizing relay 93 to open the seizecircuit of the switchboard control equipment to prevent a transmitterplugged into the line L2 from seizing the circuit until the call thathas been initiated from station E has been completed and the circuitreleased. At the end of the line interruption resulting from theoperation of calling key I0, as described above, the line relay 90 isreoperated and closes a circuit through its armature and front contactand the right hand outer armature and front contact of relay 9| foroperating relay 96. The energization of relay 96 applies groundpotential to the initiate circuit 91 to start one of the finder switcheshunting for the calling line in the same manner as described above inconnection with Figs. 1 and 2. It will be noted that the initiatecircuit is not closed until the end of the circuit interruption in orderto prevent the receiving reperforator RR being connected to the linewhile the line is still open.

The transmission of the calling line interruption from station B to themain oflice also releases the line relay H0 at station C for apredetermined interval to cause the operation of the busy lamp III atsaid station and to lock out the station until the line circuit isreleased by station E. Upon the release of the line relay III! at thebeginning of the calling line interruption, a circuit is closed throughthe spacing contacts thereof and the windings of relays I I5 and H6 foroperating relay I I5, relay I I6 being normally operated through acircuit including its left hand winding, the left hand outer armatureand back contact of relay II I and the second left hand armature andback contact of relay IIB. Upon the energization of relay II5, negativecut-off potential is removed from the grid of vacuum tubes I20, I22 andI23, and after a predetermined time interval, somewhat less than theinterval for which the timing unit 80 at station E is. adjusted, tubeI22 becomes conducting to operate relay I24 in the plate circuitthereof. Relay I24 locks up through its right hand inner armature andfront contact and the inner left hand armatures and back contacts ofrelays Ill and II 8 so that, if

a longer line interruption is received, the operation of either relayII! or H8 by the associated tubes I29 and I2I will cause the release ofrelay I24. In the present instance, however, the reclosure of the linecircuit deenergizes the relay H5 and tube I2!) is maintainednon-conducting, whereas the tube I2I has been held non-conducting by thecut-off potential applied to the grid thereof through the contacts ofrelay II I. The energization of relay I24 closes a circuit through itsouter right hand armature and front contact for lighting the busy lampIII, and opens at its middle right hand armature and back contact thecircuit of relay I25 so that said relay cannot be operated to open theline circuit or initiate a call in response to the operation of thecalling key I26. Thus, the apparatus at station C is locked out whilethe line circuit is in use by station B, and the busy signal I I Iremains lighted to indicate to the attendant or operator at station Cthe busy condition of the line.

Referring again to Figs. 2, 3 and 4, the connection of an idlereperforator through the instrumentality of one of the finder switchesSI and S2 to the calling line applies battery potential through thesecond right hand armature and front contact of relay 29, the middleswitch wiper of the finder switch and the conductor I30 to the windingsof relay 98 and 92 to disconnect the line relay 9!] from the linecircuit and to initiate the transmission of the go-ahead signal tostation B, as described above in connection with the transmission of asignal to station A when an idle reperforator has been connected to theline. The operation of relay 98 also establishes circuits for openingthe line and timing the opening through the control of tube I02 inresponse to the subsequent disconnect signal. The energization of relay92 closes a circuit through its right hand outer armature and frontcontact for operating relay 95 to open the sending leg of the terminalduplex set 88 at the same instant that negative cut-off potential isremoved from the grid of the vacuum tube I9I employed to time the lineinterruption for operating the go-ahead signal at station B (or stationC, in case of a call initiated from that station). When current isestablished through the relay 99 by the vacuum tube In I, the circuit ofrelay 95 is broken at the left hand armature and back contact of relay99 to reclose the line circuit.

At station B, the deenergization of the line relay 11 operates relay I8,as described above, to remove negative cut-off potential from the gridsof the vacuum tubes 80, 8I, 82 and 83. Just before the end of the linecircuit interruption, the tube BI become conducting and relay I4 in theplate circuit thereof is energized. Relay I4 becomes locked up and opensthe locking circuit of relay I6 at its inner left hand armature. Theenergization of relay I4 lights the go-ahead supervisory lamp 86 toindicate that transmission may be commenced, and at its outer left handarmature and back contact removes the short circuit around the keyboardcontacts of the printer P2. After transmission has been cornpleted, thecircuit is released and the equipment restored to normal by restoringthe key I0. At this time a line interruption is again produced under thecontrol of the timing unit 8!], but now the upper tap connection on theresistor 85 in the grid circuit of the tube is grounded through thesecond left hand armature and front contact of relay I4, thus decreasingthe time required for the grid of the vacuum tube 80 to return to apotential which will permit current fiow through the tube. The shorterline interruption indicated by the diagram of Fig. 6. The length of theline interruption corresponds to the transmission of a blank and thereceiving repertorator closes its blank-reading contacts, as describedabove, to release the associated finder switch. When the controlrelays'associated with the finder switch are restored to normal, batterypotential is removed from the conductor I30 to cause the release ofrelay 98 and the transmission of a line interruption for the purpose ofclearing out the apparatus at the calling station B and extinguishingthe busy lamp and restoring the equipment at station 0.

In view of the foregoing description, it will be evident that therelease of relay 98 operates and then releases relay 96 after atimeinterval deter mined by the adjustment of vacuum tube' I 02 and itsassociated relay I03. The release of the line relay 1! at station B forthis period of time causes the energization of relay 18, as. describedabove, to operate first to remove cut-01f potential from the tubes 80,8|, 82 and 83. The tubes 80 and 8! become conducting, but a moment laterthe tubes 82 and 83 also become conducting and the clearout relay I2 andrelay I3 are operated. As soon as the line circuit is reclosed and relayI8 deenergized, relays I2 and I3 become deenergized and the equipment atstation B is restored to normal.

Similarly, at station 0, the reception of the lon circuit interruptioncauses the energization of the clear-out timing unit I 23 and theassociated relay I21 to unlock the relay I24, extinguish the busy lampII I and restore the equipment at station C to normal. 7

In the case of a call initiated from station C'by the actuation of thecalling key I26, an idle reperforator at the main oflice'is seized andthe printer at station E locked out in substantially the same manner asdescribed above in connection with the placing of a call from station B.However, as indicated in the diagram of Fig. 6, the calling signal sentfrom station is of longer duration than that sent from station B, andthe timing unit 82 of station B which responds to the busy signal (callfrom station 0) is adjusted to require a longer circuit interruptionthan the timing unit I22 controlling the busy signal at station C. Uponthe operation of relay "I3 in response to the initiation ofa call fromstation C, the busy lamp 89 at station E is lighted and the circuit torelay II is opened to prevent its operation if key Ill should beactuated at this time. Station C receives a go-ahead signal from themain station, sends a disconnect signal and responds to a clear-outsignal from the main station, generally in the same manner as describedabove in connection with a call from station 13.

When a message is received at the main station for one of the stations Bor C onthe multistation circuit, the operator plugs the call into lineL2 at the switchboard and the transmission of the message is preceded byan automatic selection signal which renders the printer of the calledstation operative and looks out the printer of the other station. Thus,for example, assuming that the reperforator RR, Fig. 2, has recorded amessage for the station B on the line L2, the associated tapetransmitter TT is plugged into the jack J3 individual to said line.Likewise, calls for station C are plugged into jack J4 individual to theline L2. Assuming that the line circuit is not in use when the plug isinserted in the jack J3, a circuit is closed from ground at the Windingof relay 62 in the cord circuit through saidwindin-g to the lowercontacts of the plug and jack' J3, the winding of relay I3I, circuit 94extending through the armature and back contact of relay 93, and theleft hand armature and back contact of relay I34 to positive batterywhereupon the relay I3I becomes energized. The control relays andcircuits associated with the cord circuit and switchboard are not shownin detail, since they are shown in the copending application of; Lightand Blanton referred to above and are unnecessary for the understandingof the present invention. Since this circuit for seizing the line L2includes contacts of relay 93, it will be apparent that relay I3I willnot be energized until after any call which is in progress from 7 one ofthe remote stations B and C has been completed.

The energization of relay I3I closes a circuit from ground through thethird armature and front contact thereof, the left hand winding of relayI35, and the inner armature and back contact of relay I36 for operatingrelay I35. At its second armature and make-before-break contacts relayI3I transfers the line circuit through the contacts of relay I35,conductor I38 and the contacts of relay 95 to the sending relay so thatthe tape transmitter T'I will be operative to send over the line circuitL2 when the clutch-magnet circuit is closed at the end of the selectionsignals. The operation of relay I35 interrupts the sending circuit for apredetermined interval efiective to render the printerP2 at station Eoperative and to operate the busy signal at station C. The operation ofrelay I35 is timed by the vacuum tube I40, since negative cut-01fpotential is removed from the grid of said tube at the left handarmature and back contact of relay I35, and the tube I40 after apredetermined interval energizes relay I36 to break the circuit of relayI35 and thereby reclosethe line circuit. The grid leak resistor I43associated with the vacuum tube I40 has a, tapped connection to theouter armature and front contact of relay I3I so that the timing of thetube I40 is comparatively short in the case of a transmitter pluggedinto the jack J3' (see timing chart, Fig.6). In the case of atransmitter plugged into the jack J4, relays I32 and I35 are operated ina similar manner to that described above, but the tapped connection tothe resistor I43 isnot grounded so that the timin unit I40 causes alonger line interruption, operative to cut in station C and operate thebusy lamp at station E. i

In the case of the shorter line interruption, the deenergization of linerelay II at station E energizes relays. I8 and I9, as described above,and after a predetermined. time interval the timing unit causes relay 16to become energized and locked up. The energization of relay I6interrupts the left hand locking circuit of relay I9, and relay 18becomes deenergized when the line circuit is reclosed. Thedeenergization of relay 19 removes ground potential from the printermagnet of the printer P2 and said printer will respond to the printersignals received over the line L2. At station C, however, the same lineinterruption operates the line relay IIII, control relays H5 and H6, thetiming unit I22, and the associated busy. relay I24, thereby lightingthe busy lamp III. .Relay I I3 remains locked up to contacts of relays II I and I I8 so that the printer magnet of: printer P3, which isgrounded at the contacts of relay I I6, does not respond to the linesignals. The operation of relay I24 also looks the equipment, so thatthe operation of the calling key I25 will not be effective to render theprinter operative or initiate a call.

In the case of the longer circuit interruption to select station C, thetiming unit I20 operates after timing unit I22 and causes theenergization of relay II! to render the printer P3 operative,

and the busy lamp I I I is extinguished when relay I I is restored. Atstation B, however, the longer circuit interruption operates relay I3through the instrumentality of the timing unit 82 to light the busy lamp89, and the printer magnet of the printer P2 is locked against operationby the energization of the relay I9.

When the connection to the line L2 is electrically broken in response tothe end-of-messagc signal, as described in the above-mentioned copendingapplication of Light and Blanton, relay I3I becomes deenergized andopens at its third armature and front contact the locking circuit ofrelay I36, whereupon said relay becomes deenergized. The decnergizationof relay I36 open the circuit through the left hand operating winding ofrelay I31, but said relay is locked up through. the left hand armatureand front contact of said relay and the winding of relay I34 to ground,whereby relay I31 remains energized and relay I34 becomes energized assoon as relay I36 becomes deenergized. The energization of relay I34removes negative cut-off potential at its right hand armature and backcontact from the grid of timing unit IllI at the same instant that theline circuit is opened by the energization of relay I35 through acircuit including the left hand armature and front contact of relay I34.After a predetermined time interval fixed by the grid circuit of thetube I4I, the flow of current through said tube and the right handwinding of relay I31 in opposition to the left hand winding of saidrelay causes said relay to become deenergized. Thus, the timing unit Illtimes the circuit interruption employed to clear out the called stationand restore the busy lamp at the other station in the same manner asdescribed above. The deenergization of relay I31 open the circuit ofrelay I35, which in turn opens the circuitof relay I35. Thedeenergization of relay I35 recloses the line circuit in readiness forthe next call either from or to one of the remote stations B and C. Itwill be noted that the seize circuit 94 is held open at the left handback contact of relay I34 until the end of the clear-out signal toprevent another transmitter which might be plugged into the line fromObtaining a connection until the equipment is restored to normal. In thecase of a call through the jack J 4, the same clear-out signal istransmitted under the control of timing unit I4I upon the deenergizationof relay I32 when the cord circuit is disconnected.

It is contemplated that various types of control and switching equipmentmay be employed, since the invention is not limited to that shown anddescribed herein but includes modifications falling within the terms ofthe appended claims.

What is claimed is:

1. In a multi-station telegraph system, a main office or switchingcenter and a plurality of other branch stations, telegraph lines orchannels connectin said other stations to said main ofiice, switchingmeans at said main oflice for interconnecting said lines or channels,printer at said stations for efiecting communication over said lines orchannels, certain of said lines or channels having more than one branchstation serially associated therewith, means at the main ofiice forcontinuously interrupting the normal condition of such multi-stationline or channels for different periods and means responsive thereto anddependent upon the length thereof for selecting one of said branchstations and locking out the other of said stations.

2. In a multi-station telegraph system, a main office Or switchingcenter and a plurality of other stations, telegraph lines or channelsconnecting said other stations to said main ofiice, switching means atsaid main ofilce for interconnecting said lines or channels, printers atsaid stations for efiecting communication over said lines or channels,one of said lines having more than one branch station seriall associatedtherewith, means at each station on said last-mentioned line tointerrupt and close the circuit a single time to thereby initiate andcomplete a call, and means operative upon the initiation of a call fromone of the plurality of stations on a single line by a single lineinterruption for looking out and maintaining locked out the other ofsaid stations thereon.

3. In a multi-station telegraph system, a main office or switchingcenter and a plurality of other stations, telegraph lines or channelsconnecting said other stations to said main oflice, switching means atsaid main office for interconnecting said lines or channels, means atsaid stations for eiTecting communication over said lines or channels,one of said lines or channels having a p1urality of stations in seriesthereon, said last-mentioned line or channel terminating in a pluralityof jacks at said main ofiice equal in number to the number of branchstations thereon, means dependent upon the connection to one or theother of said jacks for interrupting the line circuit for respectivedifferent lengths of time and means responsive to such interruptions toeffect selection of a desired station on said line or channel.

4. In a multi-station telegraph system, a main cfiice or switchingcenter and a plurality of other stations, telegraph lines or channelsconnecting said other stations to said main office, certain ones of saidlines or channels serially connecting more than one of said otherstations with said main ofiice, terminals at said main ofiice for eachof said multi-station lines or channels equal in number to stationsconnected thereto, telegraph signal storage repeating means at said mainofilce, means for connecting said storage repeatin means to saidterminals and means operative 0n the connection of said repeating meansto a terminal of a multi-station line or channel to select the stationindividual thereto and lock out the other station on said line orchannel.

5. In a multi-station telegraph system, a main ofiice or switchingcenter and a plurality of other stations, telegraph lines or channelsconnecting said other stations to said main office, certain ones of saidlines or channels connecting more than one of said other stations withsaid main ofiice, terminals at said main ofiice for each of saidmulti-station lines or channels equal in number to stations connectedthereto, telegraph signal repeating means at said main ofiice, means forconnecting said repeating means to said terminals' and means operativeon the connection of a repeating means to a terminal of a multistationline or channel to select the station individual thereto and lock outthe other station on said line or channel and to prevent the operativeconnection of other repeating means at said main ofiice to'otherterminals of said line or channel. i

6. In atelegraph system, a main station or switching office, a-pluralityof branch stations,-a

telegraph line or channel connecting said branch stations in series withsaid main station, a plurality offjacks one for each of said branchstations at said main station associated with said line or channel,permutation signal transmitting means at said main station, said meansterminating in a plug insertable in said jacks to sheet transmission ofpermutation signals over said line or channel, a line interrupting meansat said main station, means operative on the insertion of said plug inany one of said jacks to control said line interrupting means tointerrupt said line or channel prior to the transmission of permutationsignals thereover, and means dependent upon the jack into which saidplug is inserted to determine the length of time said line interruptingmeans interrupts said line or channel.

7. In a telegraph system, a main station or switching oflice, aplurality of branch stations, a telegraph line or channel connectingsaid branch stations in series with said main station, a plurality ofjacks one for each of said branch stations at said main stationassociated with said line or channel, permutation signal transmittingmeans at said main station, said means terminating in a plug insertablein said jacks to effect transmission of permutation signals over saidline or channel, a line interrupting means at said main station, meansoperative on the insertion of said plug in any one of said jacks tocontrol said line interrupting means to interrupt said line or channelprior to the transmission of permutation signals thereover, meansdependent upon the jack into which said plug is inserted to determinethe length of time said line interrupting means interrupts said line orchannel, means responsive to line interruptions at said branch stationsand means controlled by said last-mentioned means to select the branchstation on said line or channel represented by the jack into which saidplug is inserted at said main omce.

3. In a telegraph system, a main station or switching ofiice, aplurality of branch stations, a telegraph line or channel connectingsaid branch stations in series with said main station, a plurality ofjacks one for each of said branch stations at said main stationassociated With said line or channel, message signal transmitting meansat said main station, said means terminating in a plug insertable insaid jacks to effect transmission of message signals over said line orchannel, a line interrupting means at said main station, means operativeon the insertion of said plug in any one of said jacks to control saidline interrupting means to interrupt said line or channel prior to thetransmission of permutation signals thereover, means dependent upon thejack into which said plug is inserted to determine the length of timesaid line interrupting means interrupts said line or channel, stationselecting and looking out means at each of said branch stations andmeans controlled by the line interruptions transmitted from said mainstation to select the branch station represented by jack into which saidplug is inserted and to lock out the other of said branch stations.

9. In a multi-station telegraph system, a main ofiice r switchingcenter, a plurality of branch stations, telegraph lines or channelseach'connecting a plurality of said branch stations to said main ofilce,switching means at: saidmain ofiice for interconnecting said lines orchannels, message signal' transmitting and receiving means at saidbranch stations for. effecting communication over said'lines. orchannels, message signal receiving and storing devices .at' said mainoffice for receiving and storing message signals from said branchstations, means to automatically and temporarily connect a messagesignal receiving and storing device to a line or channel in response toa call consisting of a single line interruption from a branch station onsaid line or channel, and means to lock out the others of said branchstations while said message signal receiving and storing device isconnected to said line or channel in response to the call from thecalling branch station.

10. In a multi-station telegraph system, a main oifice or switchingcenter, a plurality of branch stations, telegraph lines or channels eachconnecting a plurality of said branch stations to said main ofiice,switching means at said main oifice for interconnecting said lines orchannels, permutation signal transmitting and receiving means at saidbranch stations for efiecting communication over said lines or channels,permutation signal receiving and storing devices at said main office forreceiving and storing permutation message signals from said branchstations, means to automatically and temporarily connect apermutation'signal receiving and storing device to a line or channel inresponse to a call consisting of a single line interruption from abranch station on said line or channel, and means to indicate at theothers of said branch stations on said line or channel when apermutation signal receiving and storing device at said main ofiice isconnected to said line or channel in response to a call from the callingbranch station.

11. In a multi-station telegraph system, a main office or switchingcenter, a plurality of branch stations, telegraph lines or channels eachconnecting a plurality of said branch stations to said main office,switching means at said main oflice for interconnecting said lines orchannels, permutation signal transmitting and receiving means at saidbranch stations for effecting communication over said lines or channels,permutation signal receiving and storing devices at said main office forreceiving and storing permutation message signals from said branchstations, means to automatically and temporarily connect a permutationsignal receiving and storing device to a line or channel in response toa call consisting of a single line interruption from a branch station onsaid line or channel, means to lock out the others of said branchstations while said permutation signal receiving and storing device isconnected to said line or channel in response to the call from thecalling branch station, and means t indicate at the calling station whenthe connected permutation receivingand storing device has beendisconnected from said line or channel.

12. In a multi-station telegraph system, a main office or switchingcenter, a plurality of branch stations, telegraph lines or channels eachconnecting a plurality of said branch stations to said main oflice,switching means at said main oiiice for interconnecting said lines orchannels, permutation signal transmitting and receiving means at saidbranch stations for eiiecting communication over said lines or channels,permutation signal receiving and storing devices at said main ofiice forreceiving and storing permutation message Signals from said branchstations, mean responsive to a calling branch station'for connecting anidle permutation signalv receiving and storing device to the associatedlineor channel and locking out the other of said branch stations onsaidhne or channel, means at the calling branch station to 5initiate'disconnection of the connected permutation signal receiving andstoring device from the

